The present invention relates to the field of semiconductor fabrication; more specifically, it relates to a method for forming recessed polysilicon contacts in semiconductor devices.
During manufacture of semiconductor chips, transistors, diodes, capacitors and resistors along with other devices formed in the silicon portion of the chip must be interconnected to one another to form circuits. Modern semiconductor chips utilize planer technology for these interconnections. In planer interconnect technology, an insulating layer is formed on the chips surface, a trench is formed in the insulator, filled with conductor and the insulator and conductor co-planarized flat. This may be repeated many times to build up the necessary level of device interconnections required in a modern semiconductor chip.
In certain cases, it is desirable for the conductive wires to be formed from materials that are detrimental to the active devices. In these cases, the trench is filled with polysilicon. Filling the trench with polysilicon can lead to high contact resistance. Therefore recessed polysilicon contact technology has been developed. In recessed polysilicon technology the upper portion of the polysilicon is removed from the trench before the conductive wires are formed. However, as the depth to width aspect ratio of polysilicon contacts has increased, mainly due to increasing density and decreasing contact widths, several types of defects have occurred which can cause yield and reliability failures.
The first defect type is a void in the polysilicon. Voids may reach so deep into the recessed polysilicon contact that the conductive wire may contact the active device directly or they may simply increase the resistance of the contact because there is less material. Another type of defect is a polysilicon spike. Spikes are regions of polysilicon reaching up into the conductive wire and can increase the resistance of the contact.
Thus, there is a need for a method of forming recessed polysilicon contacts in which void and spike defects are greatly reduced or eliminated.
A first aspect of the present invention is a method of forming a recessed polysilicon contact, comprising: forming a trench in a substrate; overfilling the trench with polysilicon; removing the polysilicon outside of the trench to provide a substantially planar surface; oxidizing the surface of the polysilicon in the trench using plasma oxidation; and removing an upper portion of the polysilicon from the trench.
A second aspect of the present invention is a method of forming a recessed polysilicon contact, comprising: forming a trench in an insulating layer down to a conductive layer; overfilling the trench with polysilicon; removing the polysilicon outside of the trench to form a polysilicon contact in the trench to the conductive layer, a top surface of the polysilicon contact co-planer with a top surface of the insulating layer; oxidizing the a top surface of the polysilicon contact using plasma oxidation; and removing an upper portion of the polysilicon contact from the trench to form the recessed polysilicon contact to the conductive layer.
A third aspect of the present invention is a recessed polysilicon contact prepared by the process comprising: forming a trench in a substrate; overfilling the trench with polysilicon; removing the polysilicon outside of the trench to provide a substantially planar surface; oxidizing the surface of the polysilicon in the trench using plasma oxidation; and removing an upper portion of the polysilicon from the trench.